Nighttime visibility of objects and people is continuing problem, particularly for the operators of vehicles such as trucks and automobiles. Approaches to increasing the nighttime visibility of objects and people can be either passive or active. Active systems provide conspicuity by providing a steady light source, flashing light source, or a combination of steady and flashing light sources. Although active systems do provide conspicuity, they must be provided with energy, typically electrical energy, to provide the desired light. Energy sources are not always available or they may be depleted such that the light sources will not operate. As a result, active systems find limited application for providing long term conspicuity of objects and people.
Passive systems for providing conspicuity include diffuse reflectors and retroreflectors. Retroreflectors can return a significant portion of incident light back towards a light source, such as the headlights of a car or truck. Retroreflectors are typically constructed of beads (see, e.g., U.S. Pat. Nos. 4,025,159 to McGrath; 4,983,436 to Bailey et al.; and 5,066,098 to Kult et al.) or they can include cube corner elements (see, e.g., U.S. Pat. Nos. 5,272,562 to Coderre and 5,450,235 to Smith et al.). With many retroreflectors, the amount of returned light can make the retroreflective article appear as though it included a light source of its own when, in reality, at least a portion of the light directed at the retroreflector from the light source is merely being returned towards the source. Although retroreflectors return a significant portion of light, the incident light is typically from a steady source such as headlights. Steady incident light yields generally steady returned light from the retroreflectors, i.e., the intensity of the returned light does not appreciably vary.